Influence of MnO2 on the sintering behavior and magnetic properties of NiFe2O4 ferrite ceramics

Abstract The samples with small amounts of MnO 2 (0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe 2 O 3 , NiO and MnO 2 ). Microstructural features, phase transformation, sintering behavior and magnetic properties of Mn-doped NiFe 2 O 4 composite ceramics have been investigated by means of scanning electron microscopy (SEM), differential thermal analyzer, X-ray diffraction (XRD), thermal dilatometer and vibrating sample magnetometer (VSM) respectively. The XRD analysis and the result of differential thermal analysis indicate that the reduction of MnO 2 into Mn 2 O 3 and the following reduction of Mn 2 O 3 into MnO existed in sintering process. No new phases are detected in the ceramic matrix, the crystalline structure of the ceramic matrix is still NiFe 2 O 4 spinel structure. Morphology and the detecting result of thermal dilatometer show that MnO 2 can promote the sintering process, the temperature for 1 wt% MnO 2 -doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples. For 1 wt% MnO 2 -doped samples, the value of the saturation magnetization ( M s ) and coercivity ( H c ) is 15.673 emu/g and 48.316 Oe respectively.